LOWELL — When William Shakespeare bequeathed his wife his “second best bed,” was it an insult, a coded message of love, or a pro forma element in a legal document? Playwright Vern Thiessen, in “Shakespeare’s Will,” combines familiar historical facts with a wholly imagined story of life with the Bard of Avon, delivered from his wife’s point of view.

In Merrimack Repertory Theatre’s production of this one-woman show, Thiessen owes a huge debt of gratitude to actress Seana McKenna, who gives Shakespeare’s wife, Anne Hathaway, a voice and an attitude. McKenna’s performance is so luminous that she consistently lifts the script above its own mundanity.

The play opens with Anne at home on the rainy day just after she has buried her husband. Her reaction to a rumble of thunder serves as heavy-handed foreshadowing as she prepares to read the Bard of Avon’s last will and testament. Before she does, she reviews her years with, and without, her husband. Thiessen’s linear approach would be boring were it not for McKenna’s stunning ability to shift, in her storytelling, from one character to another with only a change in her voice or a turn of her head.

Very little is known about Mrs. Shakespeare, except that she was 26 and he was 18 when they met, she became pregnant, and they quickly married. Three years after the birth of their first child, Susanna, in 1583, Anne bore Shakespeare twins, named Hamnet and Judith. But William didn’t hang around long, heading to London and on tour with the King’s Men, performing and then writing for the stage. It wasn’t until his retirement, sometime after 1610, that he returned to Stratford, dying there in 1616, leaving Anne that infamous “second bed.”

With only these bare facts to start with, there’s lots of room for a playwright’s imagination to soar, yet Thiessen takes an anachronistic approach to Anne. He emphasizes her sexual experience and appetite (she lists the names of the lovers she takes during her husband’s long absences), imagines an unlikely conversation in which Anne asks the 18-year-old Will if he likes boys (“It’s OK,” she says, unfazed. “I do, too”), and — wanting it both ways — suggests the couple had both a romantic relationship and a businesslike open marriage, allowing them to live separate lives. Thiessen endows Anne with a strangely casual sense of her place in society, when in truth she was utterly dependent on her husband and her father for support.

The playwright also never gives us enough of Anne’s humanity to make us believe any of her feminist utterances. Whenever he approaches an emotional truth, such as Anne’s resentment of her busybody sister-in-law, or her exhaustion at caring for an infant alone, Thiessen short-circuits the personal connection and returns to the linear narrative. Every time Anne has a moment of self-awareness, Thiessen adds another rumble of thunder, or repairs to a flowery series of metaphors about the sea. Composer Marc Desormeaux has written two stylized songs for McKenna to sing, but they add little to the play.

Peter Hartwell creates a spare set that McKenna navigates gracefully with the help of director Miles Potter, but its abstract nature only adds another layer of distance between the audience and the character.

Ultimately, the shadow of William Shakespeare looms so large that Anne Hathaway never comes into focus, and she is again lost, not only to history, but to the imagination.